This invention relates generally to optical reading apparatus, such as a bar code reader, arranged to read coded information, characters or the like by an image sensor of electronic scanning type, and to a method of reading such optically readable information.
Among various types of optical reading apparatus a bar code reader using a charge transfer device imager or image sensor is known. When a charge transfer device image sensor is used as a transducer, a problem occurs that the output signal level from the image sensor would be low as the reading speed is increased. Namely, high-speed reading necessarily results in a short charge storage time which turns to insufficiently low output signal level, resulting in low sensitivity.
In order to increase the level of the output signal from such a charge transfer device image sensor, the intensity of incident light may be increased. However, this results in various problems, such as the increase in space occupied by the light source, power consumption and generated heat. Therefore, the intensity of incident light cannot be increased so much.